The present invention is directed to a method and apparatus for the treatment of drinking water, and more particularly to a treatment process utilizing a regeneratable ion-exchange resin in combination with an immersed membrane filter in a single process tank.
Treatment and purification of raw water in order to make it suitable for drinking can be accomplished by a number of methods. The specific contaminants of a given water stream may lend itself to the use of a particular treatment. Ion-exchange resins are used in water treatment systems in order to remove dissolved compounds, some of which are organic. Microfiltration and Ultrafiltration membranes are used to remove particulates. For a water stream that contains both these components, one treatment must be used, followed by the second. The need for two separate steps is time-consuming, requires additional equipment, and increases the overall cost of the treatment system. Accordingly, there remains a need for an improved drinking water treatment system that can remove particulates and dissolved organic compounds and which is cost- and time-effective compared to present systems.
Benedek, U.S. Pat. No. 6,027,649, discloses the treatment of drinking water in a single reactor tank using a ZEWEED(copyright) submerged membrane filter in conjunction with a flocculent mixed in the reactor tank and maintained in suspension by use of an air bubbler. The flocculent is intended to remover organics, color, bacteria, cysts and other impurities. Use of the flocculent taught by Benedek requires maintaining pH in a range from 5-9. This may require addition of acids or bases to a raw water supply to maintain the necessary pH range. While Benedek teaches a single tank using a flocculent in combination with a membrane filter, use of the flocculent for organic removal requires subsequent disposal of the spent flocculent. Thus, not only must suitable disposal for the spent flocculent be arranged, new coagulants must be provided to the reactor tank to form the necessary flocculent. Benedek also discusses the desirability of adding activated carbon to the reactor tank for the removal of dissolved organics. However, as with the flocculent, this creates disposal problems for spent activated carbon and requires replenishment of the reactor tank with new activated carbon.
Daly, U.S. Pat. No. 6,120,688, is directed to a water purification method also utilizing a ZEWEED(copyright) membrane filter. More particularly, Daly teaches initial particulate removal using the ZEWEED(copyright) filter followed by application of reverse osmosis to the filtered water. While Daly eliminates the disposal problems associated with the flocculent and activated carbon of the Benedek patent, the Daly patent requires a two step treatment process which increases plant size and cost requirements.
The present invention is directed to overcoming one or more of the problems discussed above.
The first aspect of the present invention is a method for treating drinking water. Raw water is provided to a process tank. An ion-exchange resin is added to the process tank to form a raw water/ion-exchange resin mixture. Treated water is removed from the process tank through a membrane filter. The ion-exchange resin is preferably a magnetic ion-exchange resin. This magnetic ion-exchange resin is separated from the raw water/ion-exchange resin mixture using a high gradient magnetic filter. The separated ion-exchange resin is then preferably regenerated and then re-supplied to the process tank. The ion-exchange resin may be regenerated in an external counter current column. Alternatively, the regeneration step is performed in the process tank by adding a saline solution to the process tank. Thereafter, the regenerated ion-exchange resin is separated from the raw water/regenerated ion-exchange resin mixture.
Another aspect of the present invention is an apparatus for treating drinking water. The apparatus includes a process tank for receiving a raw water. An ion-exchange resin supply is operatively associated with the process tank to provide ion-exchange resin to the raw water within the process tank. A membrane filter is operatively associated with the process tank for separating particulate matter from treated water removed from the process tank through the membrane filter. The apparatus may also include a resin separator operatively associated with the process tank for removing ion-exchange resin from an ion-exchange resin/raw water mixture. In this embodiment the ion-exchange resin is preferably a magnetic ion-exchange resin and the resin separator is preferably a high gradient magnetic filter. A resin regenerator preferably receives the removed ion-exchange resin from the separator to regenerate the ion-exchange resin through the use of a saline solution. A conveyer is then preferably provided for conveying the regenerated ion-exchange resin to the ion-exchange resin supply. The resin regenerator may be an external counter current column using a saline solution to regenerate the ion-exchange resin. In a highly preferred embodiment, an aerator is provided in the process tank for agitating an ion-exchange resin/raw water mixture in the process tank.
The apparatus and method for treatment of drinking water of the present invention combines two separate treatment technologies in a single tank for removing dissolved contaminants and particulates in a single treatment process. The apparatus and method uses an ion-exchange resin which can be separated from a raw water/ion-exchange resin mixture and then regenerated for reuse. This process both extends the useful life of the ion-exchange resin and minimizes waste generation and disposal problems that have plagued prior art water treatment systems.